Fuse and holder with rejection feature

ABSTRACT

A fuse holder substantially in the shape of a tubular receptacle intended for insertion into it of a cartridge fuse having plug terminals, and the fuse itself inserted into it, are provided with cooperating rejection means for precluding insertion of an improper fuse into the receptacle. To this end the receptacle is provided with at least one internal groove extending in a direction longitudinally thereof and the fuse is provided with at least one radial pin the outer end of which projects beyond the casing of the fuse and into the aforementioned internal groove in said receptacle.

United States Patent [1 1 Di Marco et all June 4, 1974 FUSE AND HOLDER WITH REJECTION FEATURE [76] Inventors: Bernard Di Marco, l 1 l6 Milligan,

Bellefontaine, Ohio 4331 1; Kenneth W. Swain, PO. Box 37, Hampton Falls, NH. 03844; Andrew J. Kralik, 9l 1 Sherwood, Marysville,

Ohio 43040 [22] Filed: Jan. 16, 1973 [2]] Appl. No.2 324,193

[52] US. Cl. 337/226, 337/209 [51] Int. Cl. HOlh 85/24 [58] Field of Search 337/209, 226, 225; 3l7/ll9 [56] References Cited I UNITED STATES PA'IEN'IS l.982,032 ll/l934 Stoehr 337/225 Gryftko et al 337/226 X FOREIGN PATENTS OR APPLICATIONS 161,677 7/l933 Switzerland 337/226 Primary Examiner-J. D. Miller Assistant Examiner-Fred E. Bell Attorney, Agent, or FirmErwin Salzer 5 7 ABSTRACT A fuse holder substantially in the shape of a tubular receptacle intended for insertion into it of a cartridge fuse having plug terminals, and the fuse itself inserted into it, are provided with cooperating rejection means for precluding insertion of an improper fuse into the receptacle. To this end the receptacle is provided with at least one internal groove extending in a direction longitudinally thereof and the fuse is provided with at least one radial pin the outer end of which projects beyond the casing of the fuse and into the aforementioned internal groove in said receptacle.

6 Claims, 5 Drawing Figures SHEET 1 [IF 2 PATENTEDJuu 41914 BACKGROUND or THE INVENTION In view of the continuous increase of the magnitude of available major fault currents in industrial and other systems it is necessary, to an ever increasing extent, to protect electrical apparatus, e.g. circuit breakers, by means of current-limiting fuses. This results in increased space requirements in places where space is at a premium. On panel-boards and in other locations there are generally less stringent space limitations in regard to depth than in regard to front surface. Many prior art arrangements of current-limiting backup fuses for circuit breakers have relatively large requirements in regard to front surface, and relatively small requirements as to depth, and are thus not in agreement with actually prevailing space limitations. It is, therefore, one of the objects of this invention to provide a fuse and fuse holder combination which is in better agreement with actually prevailing space limitations, and more in agreement with the teachings of U.S. Pat. No. 2,950,370 to K.W. Swain, Aug. 23; 1960 for CIRCUIT INTERRUPTING BUILDING BLOCKS.

In this country fuses having plug terminals are widely accepted. In fuses of this description the tubular casing of insulating material is closed on both ends by plug ter-. minals which are pressfittedinto the casing and held in position by steel pins projecting transversely through the easing into the plug terminals. It is, therefore, another object of this invention to provide fuse and fuse holder combinations having rejection means particularly suited for fuses of the above description.

Another object of the invention is to provide fuse holders which will accept only one specific fuse out of a family of fuses having plug terminals, and reject all other members of that family of fuses, and which fuse holder can readily be adapted to accept another specific fuse out of the family of fuses having plug terminals, and when so adapted rejects all other members of that family except said another specific fuse.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an exploded isometric view of a fuse and fuse holder combination embodying this invention and also showing a portion of a molded case circuit breaker intended to be backed up on occurrence of major fault currents;

FIG. 2 is a diagrammatic top-plan view of a fuse holder as shown in FIG. 1 without any fuses therein;

FIG. 3 is a top-plan view of a fuse embodying this in- 'vention;

FIG. 4 is substantially a longitudinal section of the fuse of FIG. 3, and

7 FIG. 5 are traces illustrating the operation of the composite circuit breaker and fuse shown in FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawings, reference character 1 has been applied to designate a tubular casing of a current-limiting fuse. Casing 1 is of an electric insulating material, e. g. melamine glass cloth. The ends of casing 1 are closed by a pair of plug terminals 2, which are press-fitted into casing 1. Steel pins 3a, 3b, 3c, 3d project transversely through casing 1 into plug terminals 2, thus affixing firmly the latter to the former. Plug terminals 2 are conductively interconnected by fusible elements or fuse links 4in ribbon form. The particular configuration of the fuse links 4 shown in FIG. 4 is more fully disclosed in U.S. Pat. No. 3,394,333 to P. C. Jacobs, Jr., July 23, 1968 for ELECTRIC FUSE HAV- ING STRESS-REDUCING FUSE LINK MEANS. Each fuse link 4is sandwiched between a pair of plates 40 of insulating material forcontrolling the arc-voltage generated incident to blowing of the fuse as more fully explained in U.S. Pat. No. 2,964,604 to P. C. Jacobs, Jr. et al, Dec. 13, 1960 for CURRENT LIMITING FUSES HAVING COMPOUND ARC-VOLTAGE GENER- ATING MEANS. The axially inner surfaces of plug terminals 2 are provided with grooves engaged by the axially outer ends of fuse links 4. The aforementioned grooves are filled with soft solder to conductively connect fuse links 4 and plug terminals 2. Fuse links 4 are shunted by a high resistance restraining wire 6 for a blown fuse indicator of the kind more fully disclosed in U.S. Pat. No. 3,391,369 to F. .I. Kozacka. July 2, 1968 for HIGH VOLTAGE FUSE. Fuselinks 4 are further shunted by a helically wound resistance wire 5'.The ends of the latter are inserted into recesses in plug terminals 2 and conductively connected to the latter by tin free solder joints. The object of resistor 5 will be set forth below. This resistor S is not our joint invention. It is claimed in a copending patent application of Frank W. Kussy et al, filed Sept. 4, I973 Ser. No. 394,290 for ELECTRIC CURRENT LIMITING LOW VOLTAGE FUSE. The upper plug terminal 2 is provided with a wire connector generally indicated by reference numeral 7 and including the set-screw 8. The lower plug terminal 2 is provided with a substantially Z-shaped terminal strap 9 i.e., a connector strapsimilar in shape to an inverted Z- affixed to it by screws 10. Connector straps 9 include web-portions extending parallel to the axis of easing l and pairs of flange portions extending at angles of in opposite directions away from the web portions. The upper flange portion of each terminal strap 9 forms a lug intended to engage a corresponding terminal in the molded case circuit breaker 11 shown in FIG. 1. Reference numeral 12 has been applied in FIG. 1 to indicate a screw intended to screw the upper flange portion of terminal strap 9 against a cooperating contact surface forming part of the molded case circuit breaker 11. The molded case circuit breaker 11 is provided with a fuse holder or pouch generally indicated by reference numeral 13. Fuse holder or pouch 13 is a molding of a plastic material or synthetic resin forming three substantially tubular receptacles 13a for insertion of a fuse into each of them. Each receptacle 13a may be provided with one or more internal groove means extending in a direction longitudinally thereof. One or more of the fastener pins 3a-3d for fastening the lower plug terminal 2 (FIGS. 3 and 4) to casing l project radially outwardly beyond thecylindrical surface of casing 1. Therefore a receptacle 13a can only receive a fuse conforming to its shape and size if there is a groove 14 juxtaposed to pins 3a-3d projecting beyond the general outline of the fuse. It is possible to vary the number of projecting pins and the position thereof, and to provide fuse holders 13 which have grooves 14a whose number and position corresponds to the number and position of the pins of the particular fuse that is intended to be accepted by the fuse holder.

a fuse can only be inserted into the fuse holder if both have corresponding projecting pins 3a-3d and pinengaging groovesil' .4. I

In FIG. 2 the possible positions of four grooves 14ahave been indicated and numbered 1', 2', 3, 4'. Considering a fuse holder 13 with a single groove having the position 1' and a fuse having one single projecting pin 3a, pin 3a cannot engage the groove positioned at I because the fuse is positioned relative to fuse holder 13 by straps 9 of the former and the slots 15 of the latter. A fuse having a single projecting pin 3a positioned as shown in FIG. 3 can only be inserted into a fuse holder having groove means positioned at 4'.

It will be apparent from the above that the present invention makes it possible to achieve a large number of combinations resulting in acceptance and rejection, respectively, of conforming tubular fuse receptacles and fuses. This is necessary for the particular coordination of fuses and circuit breakers which will be described below.

it is possible to coordinate circuit breakers and current-limiting back-up fuses for the latter either mechanically or electrically. In the first mentioned instance blowing of the fuse results in the release of a striker pin which operates a tripping bar which, in turn, unlatches the latch mechanism of the circuit breaker. The above referred-to mechanical coordination method has two limitations: It requires additional parts and requires a special circuit breaker operating mechanism. Conventional electrical coordination of a-circuit breaker and current limiting back-up fuses calls for certain values of the let-through current, and more particularly certain F1 values thereof which cannot always be met. Either the tripping or unlatching time of the circuit breaker may be too long to cause tripping of the circuit breaker by the let-through current of its back-up fuse, or the desired current-limiting action of the backup fuses could not be achieved if they were selected with the object in mind of causing tripping of a given circuit breaker by the let-through current thereof.

The resistor of FIG. 4 makes it possible to achieve electrical coordination of a circuit breaker and of its back-up current limiting fuses even in instances where the circuit breaker is relatively slow and where the letthrough 1*"! value of the fuses is relatively small.

FIG. 5 explains more in detail the operation of shunt resistor 5. FIG. 5 is a plot of current versus time, i being the trace of an available short-circuit current i being the trace of the actual short-circuit current or, in other words, that of the available short-circuit current as modified by the operation of the fuse. The actual shortcircuit current i rises initially at the same rate as the available short-circuit current i and the former decays rapidly following melting and vaporization of the fusible elements 4. After reaching an initial current zero the fault current limited by resistor 5 continues to flow for a period of time sufficient .to cause tripping of the molded case circuit breaker 11.

We claim as our invention:

1. A combination of a fuse holder and of an electric fuse including a a substantially tubular receptacle for the casing of said fuse, said receptacle being provided with internal groove means extending in a direction longitudinally thereof, and

b an electric fuse having a substantially tubular insulating casing inserted into said receptacle, said casing of saidfuse being closed at the ends thereof by a pair of plug terminals being pinned by pin means to said casing, and said fuse including at least one said pin means having a radially outer end projecting into and engaging said internal groove means in said receptacle. 2. A combination as specified in claim l'wherein said receptacle and said fuse include abutment means additional to said groove'means and pin means precluding insertion of said easing into said receptacle in any relative angular position but one 3. A combination as specified in claim 2 wherein said receptacle is provided with a lateral slot and said fuse with a connector strap projecting through said slot and determining the angular position of said fuse relative to said receptacle.

4. A combination as specified'in claim 1 wherein said receptacle has a plurality of angularly displaced internal groove means, and wherein said fuse includes a plurality of angularly displaced pin means having radially outer ends each projecting into and engaging one of said plurality of groove means. b

5. A combination as specified in claim 1 including a a molding of a synthetic resin defining a plurality of substantially tubular receptacles closed at the bottom and open at the top thereof, each of said plurality of receptacles being closed at the front and provided with a slot at the rear thereof, and each of said plurality of receptacles having at least one internal groove means extending in a direction longitudinally thereof; and

b a plurality of electric fuses each having a tubular casing inserted into one of said plurality of receptacles, said casing of each of said plurality of fuses being closed at the ends thereof by a pair of plug terminals pinned to said casing, each of said pair of plug terminals of said plurality of fuses including an upper plug terminal and a lower plug terminal, each of said plurality of fusesbeing provided with a connector strap having a web portion and a pair of flange portions extending in opposite directions away from said web portion, one of said pair of flange portions of said connector strap of each of said plurality of fuses engaging said lower plug terminal thereof and the other of said pair of flange side said casing, fusible element means inside said casing embedded in said filler, a pair of plug terminals conductively interconnected by said fusible element means plugging thevends of said casing, pin means projecting through said casing into said pair of plug terminals, and said pin means including at least one pin having a radially outer end projecting beyond the outer surface of said casing.

fggg UNITED STATES PATENT OFFICE CERTIFICATE CQRRECTIQN Dated June 4, 1974 Patent No, 3 81:, 019

Inventor(s) Bernard DiMarco et a].

It is'certified that error appears in the. above-identified patent and that said Letters Patent are hereby corrected as shown below:

r- The following should appear on the cover page, left column, aft er'line 8.

K 73' 1 Assigneez' I-T-E Imperial Corporation, Springhouse,

' Pennsylvania, of the interest ofBernard DiMarco and Andrew J. Kralik and The fihase-Shawmut Company, Newburyport, Massachusetts, of the interest of Kenneth W. Swain. Y

Signed and sealed this 19th day of November 1976" (SEAL) Attest:

McCOY M. GIBSON JR. c; MARSHALL DANN Attesting Officer Commissioner of Patents gigg y I UNITED STATES PATENT OFFICE CERTIFICATE CQRREQTEON Patent No. 3 315 ()7? Dated June 1974 Inventor(s) Bernard DiMarcO at al It iscertified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

' The following shonld appear on the eover page, left column, after line 8.

I 73' Assigneez I-T-E Imperial Corporation, Springhouse,

' Pennsylvania, of the interest ofBernard DiMarco and Andrew J. Kralik and The v{final se- Shawmut Company, Newburyport, Massachusetts of the interest of Kenneth W. Swain.

Signed ancl sealed this 19th day of November 197 s.

(SEAL) Attest:

MCCOY M. GIBSON 3R, c. MARSHALL DANN Attesting Officer Commissioner of Patents 

1. A combination of a fuse holder and of an electric fuse including a a substantially tubular receptacle for the casing of said fuse, said receptacle being provided with internal groove means extending in a direction longitudinally thereof, and b an electric fuse having a substantially tubular insulating casing inserted into said receptacle, said casing of said fuse being closed at the ends thereof by a pair of plug terminals being pinned by pin means to said casing, and said fuse including at least one said pin means having a radially outer end projecting into and engaging said internal groove means in said receptacle.
 2. A combination as specified in claim 1 wherein said receptacle and said fuse include abutment means additional to said groove means and pin means precluding insertion of said casing into said receptacle in any relative angular position but one.
 3. A combination as specified in claim 2 wherein said receptacle is provided with a lateral slot and said fuse with a connector strap projecting through said slot and determining the angular position of said fuse relative to said receptacle.
 4. A combination as specified in claim 1 wherein said receptacle has a plurality of angularly displaced internal groove means, and wherein said fuse includes a plurality of angularly displaced pin means having radially outer ends each projecting into and engaging one of said plurality of groove means.
 5. A combination as specified in claim 1 including a a molding of a synthetic resin defining a plurality of substantially tubular receptacles closed at the bottom and open at the top thereof, each of said plurality of receptacles being closed at the front and provided with a slot at the rear thereof, and each of said plurality of receptacles having at least one internal groove means extending in a direction longitudinally thereof; and b a plurality of electric fuses each having a tubular casing inserted into one of said plurality of receptacles, said casing of each of said plurality of fuses being closed at the ends thereof by a pair of plug terminals pinned to said casing, each of said pair of plug terminals of said plurality of fuses including an upper plug terminal and a lower plug terminal, each of said plurality of fuses being provided with a connector strap having a web portion and a pair of flange portions extending in opposite directions away from said web portion, one of said pair of flange portions of said connector strap of each of said plurality of fuses engaging said lower plug terminal thereof and the other of said pair of flange portions of said connector strap of each of said plurality of fuses extending through said slot in one of said plurality of receptacles, and said lower plug terminal of each of said plurality of fuses being provided with at least one pin means having a radially outer end projecting into and engaging said groove means in one of said plurality of receptacles.
 6. An electric fuse including a tubular casing of insulating material, a pulverulent arc-quenching filler inside said casing, fusible element means inside said casing embedded in said filler, a pair of plug terminals conductively interconnected by said fusible element means plugging the ends of said casing, pin means projecting through said casing into said pair of plug terminals, and said pin means including at least one pin having a radially outer end projecting beyond the outer surface of said casing. 